A Texas mother had a one-in-70-million kind of Valentine's Day this year when she gave birth to two sets of identical twin boys, a Houston hospital announced on Monday.

The four brothers were delivered at 31 weeks to Tressa Montalvo, 36, via Cesarean section at The Woman's Hospital of Texas in Houston, according to a news release from the hospital.

Tressa and Manuel Montalvo Jr. were not using any fertility drugs and had just hoped for a little brother or sister for their 2-year-old son, Memphis, according to the release.

"We planned the pregnancy - I guess we just succeeded a little too much!" said Tressa Montalvo, quoted in the release.

When Montalvo was 10 weeks pregnant, her physician told her she was having twins, and on a subsequent visit, the doctor detected a third heartbeat. The Montalvos were later informed they were having four babies - not quadruplets but two sets of twins.

The odds of delivering two sets of naturally occurring identical twins is somewhere in the range of 1 in 70 million, according to the hospital. Two boys shared one placenta and the two other boys shared another placenta.